Studies of the implementation of efficacious HIV prevention interventions are relatively rare, especially in international settings, but are critically important since they have the potential to increase the public health impact of interventions by improving uptake and sustainability. Few implementation studies have focused on provider and organizational factors (e.g., acceptability of program to staff, extent of organizational support for change) that may influence uptake and fidelity to core components of interventions. We propose to study the implementation of an efficacious intervention to reduce STIs among female sex workers (FSWs). In a previous study we developed a brief 35-minute intervention, Mujer Segura, which was delivered by community-based counselors; this intervention significantly reduced STI/HIV incidence by 40%. The Mexican federal government supports the scaling-up of this intervention across the country, and has encouraged us to formally evaluate this process. We propose to test an implementation model for transporting Mujer Segura into Community Based Organizations (CBOs) in Mexico. We have partnered with MexFam, a non-governmental organization that has CBOs throughout Mexico. Our specific aims are to: 1) Determine if our implementation model can achieve high levels of intervention fidelity and provider competency in the context of a large-scale implementation effort; 2) Characterize the relationship between individual provider characteristics and organizational factors and determine their impact on the implementation of Mujer Segura using a mixed-methods (quantitative and qualitative) approach; 3) Determine whether the implementation of Mujer Segura by CBOs is associated with decreased sexual risk behaviors among Mexican FSWs over a six-month period (e.g., increased condom use with clients, reductions in STI incidence); and 4) Determine whether improvements in sexual risk behaviors among Mujer Segura FSWs are associated with variations in intervention fidelity and counselor competency. This project will collect systematic data on the implementation process and test a model that could generalize to future implementation efforts involving Mujer Segura and other evidence-based interventions in resource- constrained settings. Our binational research team is poised to conduct this research, which will provide critical insights into barriers associated with implementing interventions in CBOs. PUBLIC HEALTH RELEVANCE: This project seeks to determine the conditions that are most conducive to the widespread adoption by community-based organizations (CBOs) of effective programs for reducing the spread of HIV and other sexually transmitted infections (STIs). Taking a brief, single-session counseling program (called Mujer Segura) that has been proven effective in reducing HIV and STIs in female sex workers who work in Mexican cities along the U.S. border, this project will study the implementation of the program in CBOs in 12 additional cities throughout Mexico to determine how best to ensure that the program remains true to the original model and retains its effectiveness. Mexico has been chosen because HIV is a global problem that respects no international borders, and because HIV prevention programs that can be implemented in settings with limited resources are urgently needed in many parts of the world.